CN111216788A

CN111216788A - Electric power steering fuzzy correction method

Info

Publication number: CN111216788A
Application number: CN202010109081.4A
Authority: CN
Inventors: 林联伟; 焦九顺; 吕莹; 胡建敢
Original assignee: Zhuzhou Elite Electro Mechanical Co ltd
Current assignee: Zhuzhou Elite Electro Mechanical Co ltd
Priority date: 2020-02-21
Filing date: 2020-02-21
Publication date: 2020-06-02
Anticipated expiration: 2040-02-21
Also published as: CN111216788B

Abstract

An electric power steering fuzzy correction method relates to the technical field of electric power steering, and comprises the following steps: s01, setting an assistance current threshold of the EPS, integrating assistance current in real time when the assistance current is increased, and integrating the return current obtained in the previous period in real time when the assistance current is smaller than the assistance current threshold; s02, equating the integration result obtained in the step S01 as a steering wheel angle, and obtaining the current return positive base current and the return positive current through table look-up; s03, calibrating adjustment factors of left return and right return of the steering wheel, and correcting the return positive current obtained in the step S02 by using the adjustment factors; s04, the assist current and the return positive current corrected in step S03 are superimposed on each other to form a target current, and current loop control of the EPS is performed, and steps S01 to S03 are repeated. The electric power steering fuzzy correction method can improve the correction effect of the whole vehicle.

Description

Electric power steering fuzzy correction method

Technical Field

The invention relates to the technical field of electric power steering, in particular to an electric power steering fuzzy correction method.

Background

For an electric power-assisted vehicle, the aligning performance of an electric power steering system (EPS) is particularly important, and is an important index for judging the driving experience. At present, due to the limitation of cost, most of the EPS installed on class-A vehicles and surface-mounted vehicles on the market are not provided with an angle sensor, as is known, the angle sensor is an important part for the EPS to acquire the angle of a steering wheel, and without the angle sensor, the situation that the steering wheel is in aligning deficiency can occur due to the fact that a system cannot determine the aligning current of the EPS in real time according to the change of the angle of the steering wheel when the vehicle runs, and the vehicle runs at a low speed obviously.

Disclosure of Invention

The invention aims to provide an electric power steering fuzzy correction method capable of improving the correction effect of a whole vehicle.

In order to solve the technical problem, the invention provides an electric power steering fuzzy correction method, which comprises the following steps:

s01, determining the integration object: setting an assistance current threshold of the EPS, integrating assistance current in real time when the assistance current is increased, and integrating the return positive current obtained in the previous period in real time when the assistance current is smaller than the assistance current threshold;

s02, determining the current positive back current: equating the integration result obtained in the step S01 to a steering wheel angle, and obtaining the current return-to-positive basic current and the return-to-positive current through table lookup;

and S03, correcting: calibrating adjustment factors of left return and right return of the steering wheel according to the friction resistance of the steering system of the vehicle, and correcting the inherent deviation of the return current obtained in the step S02 by using the adjustment factors;

s04, current loop control: and (4) superposing the boosting current and the return positive current corrected in the step (S03) into a target current to perform EPS current loop control, and repeating the steps (S01-S03) after a certain time interval.

Further, in step S01, the boost current threshold is less than or equal to 2A.

Further, after the integration result obtained in step S01 is equivalent to the steering wheel angle in step S02, the magnitude of the return base current is determined according to the relationship table between the steering wheel angle and the base return current, and then the magnitude of the return current is determined according to the relationship table between the percentage of the return base current decreasing with the vehicle speed.

Further, in step S03, the adjustment factors for the left and right steering wheel return corrections are both 0.5-0.6.

Still further, in step S04, the positive return current is required to be controlled by a ramp, the ramp control coefficient is 0.05-0.1, and the ramp control time limit is 2-3S.

Preferably, in step S04, the time interval for repeating steps S01-S03 is 3-10 ms.

The electric power steering fuzzy correction method provided by the invention utilizes the characteristic that a motor does work equivalently in the power assisting process and the correction process, integrates the power assisting current in the power assisting process and the correction current in the correction process respectively, calculates the correction current of the electric power steering system in real time according to the driving speed of a vehicle, corrects the correction current by fully considering the friction resistance of the system, realizes the current closed-loop control of EPS, and thus, a steering wheel can return to the position close to the midpoint. The method is simple and easy to realize, and can ensure that the vehicle without the angle sensor can have better aligning effect, thereby effectively solving the problem of insufficient aligning of the traditional vehicle under low-speed running.

Drawings

FIG. 1 is a current integral equivalent diagram of a motor boosting process and a return process in an electric power steering system;

FIG. 2 is a flow chart of an electric power steering fuzzy alignment method according to the present invention;

FIG. 3 is a graph of the return basic current varying with the steering wheel angle in the electric power steering fuzzy return method according to the present invention;

FIG. 4 is a graph of percentage of return basic current drop with vehicle speed in the electric power steering fuzzy return method according to the present invention;

fig. 5 is a graph showing the change of each current with time in the electric power steering fuzzy alignment method according to the present invention.

Detailed Description

In order to facilitate understanding of those skilled in the art, the present invention will be further described with reference to the following examples and drawings, which are not intended to limit the present invention.

Before the present invention is explained, it should be noted that in the electric power steering system, the electric motor performs equivalent work in the power assisting process and the returning process, and the steering wheel can be returned to the approximate middle point by using the characteristic point. The calculation formula of the power W of the motor is as follows: w = UIt, where is the battery voltage, I is the current, and t is the working time. Because the voltage of the battery is basically kept unchanged in the whole working process of the system, the formula for doing work of the motor can be simplified for convenient calculation, namely, the current of the motor is integrated

To indicate that the motor is doing work. As shown in fig. 1, the integral of the current at the time of power assist is diagonally hatched area W1, and the integral of the current at the time of return is hatched area W2, and the return-to-positive effect can be ensured as long as W2 is approximately equal to W1.

In view of the above, the present invention provides an electric power steering fuzzy correction method for improving the correction effect of the whole vehicle, as shown in fig. 2, the electric power steering fuzzy correction method includes the following steps:

and S01, determining an integration object.

Determining whether to integrate the boosting current or integrate the return current according to the boosting current of the system, wherein the boosting current is calculated by the system according to a torque sensor, the boosting current is generated when the steering wheel is turned to the left or to the right, the system determines the integration object according to the absolute value of the boosting current, the boosting current is very small and fluctuates around a zero value at the moment from the stopping of the steering to the return, therefore, in order to enable the system to more rapidly and accurately determine the change, a boosting current threshold value is set in the system, the boosting current threshold value can be 2A, when the absolute value of the boosting current starts to increase, the angle of the steering wheel is increased, the vehicle performs the steering operation, the boosting current is integrated in real time, and when the boosting current starts to be smaller than the boosting current threshold value, the angle of the steering wheel is reduced, the vehicle starts to perform a return operation, at which time the return current obtained from the previous cycle is integrated in real time (one cycle, with very short time intervals per cycle, from steps 01-04).

S02, determining the current return positive current.

It is known that the output power of the motor is closely related to the input power of the motor, and in the same system, the output power of the motor is only related to the rotating speed of the motor, the input power depends on the current of the motor, and the corresponding relation between the current of the motor and the rotating speed can be obtained according to the relation between the output power and the input power of the motor. By using the principle, the corresponding relation between the motor current integration result of each automobile and the steering wheel angle can be obtained. As shown in fig. 5, the target current of the motor is equal to the sum of the boost current and the return positive current during the boosting process or the return positive process of the vehicle, while the return positive current is small and negative during the boosting process, so that the target current of the motor can be similar to the boost current during the process, and in addition, the boost current is zero during the return positive process, so that the target current of the motor is equal to the return positive current at the time. Accordingly, in the present embodiment, the integration result obtained in real time in step S01 may be equivalent to the steering wheel angle, the return base current may be obtained according to the corresponding relationship between the return base current and the steering wheel angle as shown in fig. 3, and the return current may be obtained according to the relationship between the percentage of the return base current decreasing with the vehicle speed as shown in fig. 4 (the graphs shown in fig. 3 and 4 are stored in the electric power steering system in advance in a table form).

And S03, correcting.

In the automobile steering system, the friction resistance between the components can affect the return effect of the steering wheel, and in order to ensure the left-right consistency of the return time, the adjustment factors of the left return and the right return of the steering wheel can be calibrated according to the friction resistance of the steering system of the automobile, and the adjustment factors are used for correcting the system inherent deviation of the return current obtained in the step S02. In the present embodiment, the adjustment factors for the left and right return-to-positive steering wheel adjustments may preferably be 0.6, and the return-to-positive current obtained in step S02 may be multiplied by 0.6 to obtain a corrected return-to-positive current.

And S04, current loop control.

In an electric power steering system, the current of a motor is controlled in a closed loop mode, and after a corrected return positive current is obtained, the power-assisted current and the corrected return positive current are overlapped to form a target current to perform current loop control on the EPS. It is worth mentioning that the return-to-positive control is not needed when the vehicle is in place, in order to enable the return-to-positive current to be smoothly transited when the vehicle starts and stops, the return-to-positive current can be subjected to slope control when the vehicle starts and stops, the coefficient of the slope control is 0.05-0.1, and the time limit value of the slope control is 2-3S. In the present embodiment, it is also important to repeat steps S01 to S03 every 5ms after the completion of the closed-loop control during the running of the vehicle in order to realize the real-time control of the electric power steering system for the blur restoration.

The above embodiments are preferred implementations of the present invention, and the present invention can be implemented in other ways without departing from the spirit of the present invention.

Some of the drawings and descriptions of the present invention have been simplified to facilitate the understanding of the improvements over the prior art by those skilled in the art, and some other elements have been omitted from this document for the sake of clarity, and it should be appreciated by those skilled in the art that such omitted elements may also constitute the subject matter of the present invention.

Claims

1. An electric power steering fuzzy correction method is characterized by comprising the following steps:

2. The electric power steering fuzzy regression method according to claim 1, wherein: in step S01, the assist current threshold is less than or equal to 2A.

3. The electric power steering fuzzy regression method according to claim 2, wherein: in step S02, after the integration result obtained in step S01 is equivalent to a steering wheel angle, the magnitude of the return-positive base current is determined according to the relationship table between the steering wheel angle and the base return-positive current, and then the magnitude of the current return-positive current is determined according to the relationship table between the percentage of the return-positive base current decreasing with the vehicle speed.

4. The electric power steering fuzzy regression method according to claim 3, wherein: in step S03, the adjustment factors for the left and right steering wheel return corrections are both 0.5-0.6.

5. The electric power steering blur restoration method according to claim 1 or 4, characterized in that: in step S04, the positive return current is required to be controlled by a ramp when the vehicle starts and stops, the coefficient of the ramp control is 0.05-0.1, and the time limit value of the ramp control is 2-3S.

6. The electric power steering fuzzy regression method according to claim 5, wherein: in step S04, the time interval for repeating steps S01-S03 is 3-10 ms.